1. Technical Field
The present invention relates to an image display system and a control apparatus.
2. Related Art
There have been known technologies for displaying video images from a projector or any other apparatus on a screen. In recent years, there has been a proposed technology for displaying video images by using a screen capable of switching its state between a transmission (transparent) state and a scatter state and projecting video image light on the screen that operates in the scatter state. Using the technology to set the screen to be transparent when no video image is projected reduces a feeling of spatial oppression produced by the screen not in use. A screen capable of switching its state between the transmission (transparent) state and the scatter state by using a liquid crystal layer has been proposed (JP-A-6-82748, for example) as an example of the screen described above.
As the technology for switching the state of a screen between the transmission (transparent) state and the scatter state by using the liquid crystal layer, there is a known polymer dispersion liquid crystal display apparatus in which a liquid crystal material is dispersed in a polymer (JP-A-10-36317, for example). The principle according to which a polymer dispersion liquid crystal display apparatus of this type operates uses the difference in refractive index between the liquid crystal material and the polymer. In a normal mode, the transmission state is created by applying an electric field, and the scatter state is created by removing the electric field. In a reverse mode, the transmission state is created by applying no electric field, and the scatter state is created by applying the electric field.
When the polymer dispersion liquid crystal display apparatus is used as a screen, and video image light is projected on the screen that operates in the scatter state, a desired image is displayed on the screen. In the related art, however, since the degree of light scattering in the scatter state is fixed, in other words, the degree of light scattering produced by the screen is the same for all displayed images, the following problem, for example, occurs.
For example, when a dark image is displayed on the screen set to allow a viewer to clearly view a bright image (with high contrast) by increasing the degree of scatter produced by the screen, the contrast of the dark image greatly lowers due to scattering of external light. Conversely, when a bright image is displayed on the screen set to reduce the effect of external light to clearly display a dark image by reducing the degree of scatter produced by the screen, the contrast of the bright image lowers. Further, since the degree of scatter is small in the latter case, high luminance portions (bright points) produced on the screen make it difficult for the viewer to view the image because it is too bright. In particular, when video images formed of bright images mixed with dark images, such as moving pictures, are displayed, it is difficult for the viewer to view the images.